This invention relates to fluid control valves, and more particularly, to ball valves used to control the flow rate of fluids, such as high pressure steam. The use of ball valves to control the flow of fluid is well known in the art. The ball component of the valve may have one or more through holes allowing fluid to pass through the ball at one or more rates. Ball valve members are typically confined between two annular sealing seats, one located upstream with respect to the ball and one located downstream. In most applications, the body which houses the ball is composed of two halves which are sealingly joined at approximately the midpoint of the ball.
Under conditions involving high temperatures and high pressures, ball valves have not been successfully used as fluid control valves because of several problems. First, the sealing seats are typically made of tetrafluoroethylene or other sealing materials which usually cannot withstand high temperatures and pressures. Additionally, when a ball valve is in a partially open position to allow for a desired minimum flow rate, because of the high pressure differential across the valve, the sealing surfaces of the sealing seats erode and cause leakage in the closed position. Additionally, in valves where the body is split at approximately the midpoint of the ball, leakage around the stem of the ball and at the interface between the two halves of the body occurs due to the turbulent forces acting at the interface between the two halves of the body.
In some high temperature and high pressure applications, mitered valves have been used, which feature the use of a globe valve or a series of discs upstream of a ball valve to regulate flow. However, mitered valves are likewise subject to erosion and leakage in high temperature and high pressure applications.
This invention overcomes the above-noted and other deficiencies of the related art, by providing a method and apparatus for allowing the selective control of the rate of fluid flow through a valve between a minimum and maximum rate, while at the same time protecting a downstream sealing seat, which is an integral part of an end cap or end housing, from damage. The ball valve of this invention is able to withstand high temperature and high pressure conditions, which other fluid control valves known in the art cannot withstand.
The invention features a valve which is capable of allowing selection between a maximum or minimum flow rate and flow rates in between. Through the use of a sacrificial annular upstream sealing seat, erosion of the integral downstream sealing seat is minimized. The invention features the use of ball, body, end cap or end housing, and sealing components made of materials able to withstand high temperatures and pressures. In another feature of the invention, the use of a body and end cap in a conformation superior to the existing art minimizes erosion and leakage around the ball. The invention eliminates the undesirable feature common to existing valves wherein they are unable to withstand high temperature and pressure conditions without leakage. The invention further eliminates the undesirable feature of accelerated damage to the downstream integral sealing seat when a ball valve is partially opened to achieve a desired minimum flow rate, or when the position of the ball valve is adjusted to change the flow rate.
The invention also features the use of two through holes of different diameters, allowing selection between a maximum flow rate, a minimum flow rate, or incremental flow rates lying between the two extremes. By providing a second through hole to allow for a minimum flow rate, the high turbulence which results when a single hole valve is placed in a partially open position to achieve a desired, minimum flow rate is avoided. The invention is thereby capable of performing precise fluid flow control, under high temperature and pressure conditions. This invention is the first ball valve which achieves the dual results of allowing a controlled variation or selection of the rate of fluid flow under high temperature and pressure conditions, while simultaneously protecting the downstream seat from damage.
The above features of the invention are accomplished by providing a ball valve disposed in a body having an end cap or end housing. Two through holes are provided through the ball of the ball valve. The first through hole is of one diameter, allowing for a maximum flow rate. The second through hole is disposed at an angle to the first through hole, and is of a smaller diameter allowing for a minimum desired flow rate. The ball of the valve is rotatable through the use of an operator around a central axis which is perpendicular to the passageway through the body in which the ball is disposed. A sacrificial annular upstream seat, having an internal diameter smaller than the diameter of the first passageway, is disposed upstream from the ball. An annular downstream sealing seat is integral to and forms part of the end cap or end housing. The downstream seat has an internal diameter which exceeds the internal diameter of the upstream seat.
Because of the pressure differential created when fluid flows past the sacrificial upstream seat, there is a reduction in the destructive forces acting on the ball and on the integral downstream seat. This sparing effect is most beneficial when the valve is in a partially open position, as it is when changing from the maximum flow rate to the minimum flow rate, or vice versa. The sparing effect of the sacrificial seat on the downstream seat is also seen when the valve is set at the maximum flow rate. When the valve is set at the minimum flow rate position, the ball itself protects the downstream seat from damage. Thus, at maximum or minimum flow rates, or rates in between, the downstream seat has greater protection than in the prior art from turbulent flow. Because the position of the through holes can be varied by rotating the ball through the use of an operator, precise flow rate can be selected at either the maximum or minimum flow rate, or at flow rates between the two extremes, under high temperature and pressure conditions, while simultaneously protecting the integral downstream seat from wear.